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CVE-2026-42897

From Exploited flaws, HARD’s guide to the flaws being used in attacks · Checked
This article is about a flaw in Microsoft. For every flaw being used in attacks, see Exploited flaws; for Microsoft’s, see Microsoft flaws being used in attacks.

CVE-2026-42897 is a security flaw in Microsoft. Attackers can run code in the browser of someone using Microsoft and act as them. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 15 May 2026.[1]

Microsoft is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Fixed in version 15.01.2507.069, 15.02.1544.041, 15.02.1748.046 and 15.02.2562.043.

Description

CISA calls it an exchange server cross-site scripting in Microsoft Microsoft. In its words: “Microsoft Exchange Server contains a cross-site scripting vulnerability during web page generation in Outlook Web Access and when certain interaction conditions are met, arbitrary JavaScript can be executed in the browser context.”[1]

The underlying weakness is cross-site scripting (CWE-79), in MITRE’s list of common software weaknesses.[2]

It scores 6.1 out of 10 on the Common Vulnerability Scoring System, which rates it medium, scored by NVD using CVSS 3.1.[2]

Affected versions

NVD’s record lists these fixed versions: in each line, everything before the version shown is affected.[2]

ProductFixed in
Microsoft Exchange Server 2016 Cumulative Update 2315.01.2507.069
Microsoft Exchange Server 2019 Cumulative Update 1415.02.1544.041
Microsoft Exchange Server 2019 Cumulative Update 1515.02.1748.046
Microsoft Exchange Server Subscription Edition RTM15.02.2562.043

Most families won’t have Microsoft; it’s for whoever looks after IT at work.

Exploitation

CISA added it to its catalog of known exploited vulnerabilities on 15 May 2026, within a day of it being made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 29 May 2026 to fix it.[1]

FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 71%. That’s in the top 1% of the flaws it scores.[4]

CISA assesses it as not automatable: each attack takes some work.

CISA doesn’t say who was attacked, or how.

Fix

Microsoft has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.”[1]

  1. Check whether you use it.Microsoft is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
  2. Send this page to your IT person.Ask them to confirm it’s fixed (fixed in version 15.01.2507.069, 15.02.1544.041, 15.02.1748.046 and 15.02.2562.043), or not in use. CISA gave US government agencies until 29 May 2026 to fix it.
  3. If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.

You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.

Timeline

DateEvent
The flaw is made public in the National Vulnerability Database, with a severity score of 6.1.[2]
CISA adds it to its catalog of flaws known to be used in attacks.[1]
CISA’s deadline for US government agencies to fix it.[1]
FIRST puts the odds of it being used in attacks in the next 30 days at 71%.[4]

See also

Other Microsoft flaws

  • CVE-2026-96951, Microsoft Windows: command injection ·
  • CVE-2026-65660, Microsoft SharePoint: code injection ·
  • CVE-2026-85880, Microsoft Windows: heap-based buffer overflow ·
  • CVE-2026-81963, Microsoft Windows: link following ·
  • CVE-2019-1068, Microsoft SQL Server: remote code execution ·

Other cross-site scripting flaws

  • CVE-2025-48700, Synacor Zimbra Collaboration Suite (ZCS): cross-site scripting ·
  • CVE-2025-66376, Synacor Zimbra Collaboration Suite (ZCS): cross-site scripting ·
  • CVE-2025-68461, Roundcube Webmail: cross-site scripting ·
  • CVE-2021-26829, OpenPLC ScadaBR: cross-site scripting ·
  • CVE-2025-27915, Synacor Zimbra Collaboration Suite (ZCS): cross-site scripting ·

Every Microsoft flaw on CISA’s list · Everything added in May 2026

References

  1. ^ Cybersecurity and Infrastructure Security Agency. “Microsoft Exchange Server Cross-Site Scripting Vulnerability”. Known Exploited Vulnerabilities Catalog, added 15 May 2026.
  2. ^ National Institute of Standards and Technology. “CVE-2026-42897 Detail”. National Vulnerability Database, published 14 May 2026.
  3. ^ Microsoft. Advisories and fixes: msrc.microsoft.com, learn.microsoft.com, msrc.microsoft.com.
  4. ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.707, percentile 99.4, 31 Oct 2026.
  5. CVE Program. “CVE-2026-42897”. The official CVE record.

This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.